I propose that content should be able to be purchased at full price up to five additional times, with each additional time it is purchased it giving another multiplier of all loot dropped in that content.
For example, one could purchase Ravenloft six times, once for 0.99 under the special and five additional times at full price, and if solo, would gain six times normal drop rate from it.
If grouped, real players replace multibox drop rate, so 4 real players, one of which has purchased content 5x get a total of 6 persons worth of loot, with the person who purchased that content 5x times getting triple loot.
If multibox purchases would exceed filling empty spots, those slots are filled by lottery of multibox slots. So four people, each of which purchased content two extra times each, fills that last two loot spots with a lottery of two drawn from the 8 multibox licenses.
Like the HP pass, this can also serve as a catch-up mechanism for new players, where they can farm out their gear sets in reduced time in a way that contributes to the game.
We can also give flavors to the multiboxes and allow the player to pick which one they want first, second, third, etc.. A bard one would start a player with bard songs. A cleric one would give divine buffs at the start. An Arti one disables all dungeon traps. A rogue one opens all dungeon locks, etc.
Basically, fully support multiboxing, making it less of a mess to use.